Back-to-school means back to backpacks — a necessity for any school-age child who must tote books and supplies from school to home.

Though some students may opt for other types of bags, such as messenger bags or tote bags, the backpack is one of the most popular ways to transport heavy materials since it is designed to distribute weight across the stronger muscles of the back.

Make the wrong choice for a backpack and you could find yourself dealing with everything from premature wear and tear to a child with back pain and poor posture.

The American Academy of Pediatrics says a backpack should not weigh more than 10 to 20 percent of the student’s total body weight. Packing heavy items toward the center will make it easier to carry.

Remind your child to use both shoulder straps, rather than slinging the pack over one shoulder, and tell him or her to carry as few books at once as possible.

When you are shopping for a backpack, look for these features:

Lots of padding. Try to find a backpack with two wide, padded shoulder straps and a padded back. Older kids may be tempted by the single strap backpacks that run across the body, but they cannot distribute weight evenly, according to the American Academy of Pediatrics. A backpack with padding on the back can make it more comfortable to carry.

A waist strap. If the backpack has a waist strap, use it. It helps distribute heavy weight even more.

How it fits. Give the backpack a test run in the store. Adjust the straps so the pack is close to the body. A backpack with the proper fit should fall about 2 inches above the waist, according to American Academy of Pediatrics guidelines.

Roll on. If the school allows rolling backpacks, consider this as a choice for children who either have to carry a lot of books, or who may have a smaller body frame. Of course, rolling backpacks must be carried up the stairs, and they can be hard to roll over grass or snow.

Think sturdy, but light. When considering materials, think lightweight, yet sturdy. Rip-Stop nylon, for example, is lightweight and its heavier threads can prevent or slow further ripping if the backpack is torn or punctured.

Update as needed. Parents may want a backpack to last forever, and certainly, some sturdier models can last more than a year. But it is more important to make sure the backpack fits your child from one year to the next. If it is too small or otherwise ill-fitting, invest in a new one.